Polymeric, conductive hydrogels have been used in medical devices to adhere the device to a patient's skin, such as biomedical electrodes to provide a secure, conductive connection between the medical device and the patient's skin for stimulation or sensing purposes. However, in certain applications such as iontophoresis devices, known hydrogel compositions possess significant disadvantages.
Iontophoresis is a method for introducing active pharmaceutical agents into a patient. The method utilizes electrical current to transport the active agents, which are usually in charged form, but may also be uncharged, through the skin, mucosa or other body surface of the patient. The iontophoresis process has been found to be useful in the administration of lidocaine hydrochloride, hydrocortisone derivatives, penicillin, dexamethasone sodium phosphate and many other pharmaceutical agents. Iontophoretic methods have also been employed to deliver uncharged therapeutic agents by the mechanism of induced solvent flow.
Iontophoretic devices employ two electrodes. The first electrode, called the active electrode, is the element from which the active agent is transported into the body. The second electrode, called the counter or ground electrode, serves to complete the electrical circuit through the body. In typical applications, the active electrode holds, contains or otherwise has available to it a source of the active agent. Thus, the active electrode is usually complex compared to the counter electrode.
U.S. Pat. No. 4,820,263 discloses a combination of an adhesive material and active agent for use as the active electrode. The adhesive material is a nontoxic, polymeric material that is or can be made tacky and can dissolve or disperse pharmaceutical agents.
Additional disclosure regarding iontophoresis devices can be found in our copending application Ser. No. 07/502,841 "Device and Method For Iontophoretic Drug Delivery" which is incorporated herein by reference.
Hydrogels are also known to be used for other medical purposes such as to secure other medical devices such as electrodes, bandages and the like to the human body and when so applied to provide necessary conductivity, wound protection, medicament delivery and other desirable properties for the operation of the device.
U.S. Pat. No. 4,904,247 discloses a pressure-sensitive hydrophilic laminate composite for wound dressing in which one layer of the laminate is a tacky hydrophilic polymer blend and a second layer is a non-tacky hydrophilic polymer blend. The tacky hydrophilic polymer layer is adapted for attachment to skin.
U.S. Pat. No. 4,391,278 discloses a skin electrode for sensing and stimulation utilizing a conductive adhesive mixture of a polymerized form of 2-acrylamido-2-methylpropane sulfonic acid or one of its salts with water and/or an alcohol for attachment of the electrode to the patient's skin.
U.S. Pat. No. 4,570,629 discloses a hydrophilic biopolymer comprising a water soluble anionic protein electrolyte component derived from keratin and a water soluble cationic biopolymer poly electrolyte component selected from glucosaminoglycan and collagen for use in treating burned human skin.
However, known hydrogels have significant disadvantages in some applications due to the ionic structure of the adhesive composition. For example, iontophoresis electrodes constructed using known ionic hydrogel adhesives readily adhere to the skin but the ionic polymer and charged pharmaceutical agent tend to combine chemically into salts, thereby causing a diminished transfer of the agent through the skin.
It is therefore an object of the present invention to provide a polymeric hydrogel having a strong, amphoteric ionic structure.
It is also an object of the present invention to provide a polymeric hydrogel which would not be a source of migrating ions.
It is also an object of the present invention to provide a hydrogel matrix for delivery of drugs.
It is also an object of the present invention to provide a polymeric, amphoteric hydrogel to which desired mobile ionic species can be added in desired amounts.
It is also an object of the present invention to provide a polymeric hydrogel adhesive that can be used in diverse medical device applications including iontophoresis devices and other devices for skin contact delivery of medicaments, sensing electrodes, stimulation electrodes and wound dressings.
It is also an object of the present invention to provide a polymeric hydrogel which can be used in implantable drug delivery devices and which can be used to improve the surface characteristics of implantable medical devices.